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KX 60 won't rev out

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Hi, my nephew has been riding his 1992 KX 60 for the last 2 years with no troubles and now all of a sudden it does not want to rev out at all. Bike starts and idles great just like before but as soon as you give it anywhere from 1/2 to full throttle it will bog and choke out, not revving like it should. Bike does this whether in neutral at a stand still or riding under a load. Bike doesn't kill from the bogging but it will simply just not make it above a certain rpm. I have cleaned the card a couple of times and everything else I have checked is ok, jetting, reeds, float height, air filter, spark plug, gas etc, Nothing on the bike changed. We were out riding when it happened. Any ideas? Thanks

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Its a kx, not a Honda!

They were all put together with their eyes squinted , different colored plastics so the factory workers wouldn't get confused to which line they were supposed to be working on.  :ride:

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Carb is plugged.

Check jets and needle and slide. Also check the air filter. Reeds too.

Already went through and cleaned the carb twice, everything checks out, same with the air filter and reeds. I also tried swapping the carb and reeds from a well running bike and the condition remained, so this leads me to believe problem is elsewhere.

 

Elevation change? Drastic change in humidity or temp? Main jet fall out? Spark plug? 

 

Same elevation, temp, humidity as always. Main jet is in tact. Tried new plug, makes no difference.

 

Done a compression test on it ? Or rebuilt the top end lately ? 

 

No rebuild recently and have not got around to checking the compression yet. I do believe that the problem lies elsewhere though.

 

Any chance it could be the ignition coil, stator, or something like an air leak? Or any simple tests I can do to help diagnose the problem?

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You can check for air leaks with starting fluid spraying it around suspected leaks ( carb boots , base gasket , case gaskets ) it will alter the idle or just kill it. Spray soap and water mix on anything you suspect it will make bubbles . Still won't be 100% like a leak down tester but it's a cheap way to check . Crank seals are less than 20 bucks in most cases and will never hurt to change them and you can do it in an hour. Coil will usually fire or not and same with a stator , or a stator will run great for 10 minutes then just stop firing altogether with heat. It wouldn't hurt to check them and can do it with a 20$ meter. All kinds of youtube videos on it but you need the service manual to get limits. 

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Does it use a kips?

Possible power valve stuck.

 

No it does not. I am leaning toward a leaking crank seal or timing issue. Going to take a look tomorrow

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Can't really tell if the seals are good or not. Think I am going to replace them just in case. Has anyone used the machine screw removal method on this bike before to avoid having to split the cases? Also do you think silicone would work as a temporary fix to seal the leak? Would like to be able to take the bike out this weekend.

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